1. Field of the Invention:
This invention concerns a magnetic storage device, concretely the magnetic storage device having the recording density over 5 gigabits per square inch and the magnetic recording medium to realize the magnetic storage device having the high output, low noise and high stability caused by suppressing the attenuation of output by moderating the thermo-magnetization.
2. Description of the Related Art:
Recently, because the recording density has been improved in the magnetic storage device for the computer, more and more noise reduction and high coercivity have been required. The minimizing the crystal grain size in the magnetic layer and the reduction of the magnetic combination of interparticles are effective for the media noise reduction. As a method for minimizing the magnetic crystal grain, forming the new layer (for example, called the seed layer) is being tried. For example of the new layer, it is shown in Japanese Open Patent Application H4-153910, that seed layer of amorphous or very small grain which consists from a kind of Y,Ti,Zr,Hf,V,Nb,Ta,Cr,Mo,W is formed. It is shown in Japanese Open Patent Application H7-73441 that magnetic crystal grain is minimized and media noise is reduced by forming seed layer of amorphous which consists from Cr or V.
A small magnetism crystal grain receives the effect of the heat disturbance. So, the phenomenon that the recorded magnetization disappears with the passage of the time becomes remarkable.
Therefore, extremely small magnetism crystal grains are not desirable because the reliability is down when the recorded data is preserved in the long term. Also, when magnetism crystal grains are minimized and the magnetic combination of the interparticle is strong, many magnetism crystal grains are inverted their magnetic direction at the same time. So the effect of reducing noise can not be obtained. So, it is necessary to reduce the exchange interaction between magnetic particles. For this purpose, it is effective to increase Cr concentration in the magnetic layer and to increase the nonmagnetic segregation region of the interface of the magnetic particles. But, magnetization reduces when the Cr concentration increases. So, the record and reproduction output reduces so much that good record and reproduction characteristic can not be obtained.
In the meantime, S. H. Liou proposed a medium that the crystal grain Fe dispersing in the amorphous SiO2 takes the Granular structure. (S. H. Liou and C. L.Chien: Appl. Phys. Lett. 52(6), Feb. 8, 1988) The Granular medium (i.e. the medium which magnetic layer takes Granular structure) has characteristics that the magnetic interaction between the magnetic particles is weak because the magnetic crystal grains are separated by the nonmagnetic phase and media noise is low because the magnetic crystal grains are very small.
As another prior art, it is shown in Japanese Open Patent Application H7-311929 that the Granular medium has a magnetic layer with magnetic crystal grains of Co alloy and nonmagnetic phase of Al2O3, TiO2, ZrO2, Y2O3. But there is a problem in Japanese Open Patent Application H7-311929 that the high coercive force is not obtained because magnetic crystal grains are too small.
It is shown in Japanese Open Patent Application H7-98835 and Japanese Open Patent Application H8-45073 that the high coercivity is realized by applying the alternating current bias during forming a film or it is heat-treated in the vacuum after forming a film.
But in the Granular medium, magnetic crystal grains are small and C axis which is easy magnetic orientation axis of magnetic crystal grains has randomly been orientated. So, as it is above-mentioned, coercive force improves to some extent by applying the alternating current bias or heat-treating. But the coercive force obtained from this Granular medium is not sufficient for the high density recording over square inch 5 gigabits. So, good record and reproduction characteristic can not be obtained because of reproduction output is low in recording at high recording density but noise is low. Furthermore, magnetic crystal grains: are so small that the phenomenon that the thermomagnetization redueases is very remarkable and the sufficient reliability in the high recording density region can not be obtained.
As is mentioned above, the Granular medium of prior art is a low noise medium but sufficient stability for the heat disturbance is necessary for the Granular medium to realize the high recording density.
A purpose of this invention is to get high coercivity and high coercivity squareness in the low noise medium which magnetic layer takes Granular structure by giving the magnetic anisotropy to circumferential direction of magnetic crystal grain in the magnetic layer. By this, it is possible to get the magnetic recording medium which has high reproducing output in high recording density and the sufficient stability for the reduction of thermomagnetization.
Furthermore, if this medium is combined with the supersensitive magnetic head and the condition of the magnetic storage apparatus is optimized, it is possible to get the magnetic storage with the high reliability and the recording density over 5 gigabits per 1 inch.
Above mentioned purpose can be obtained by the magnetic storage apparatus which comprising a magnetic recording medium having a magnetic layer with Granular structure and a magnetic crystal grain in the magnetic layer with circumferentially magnetic anisotropy, means for moving said magnetic recording medium in the recording direction, the magnetic head having recording part and reproduction part, means for moving said magnetic head relatively to said magnetic recording medium and means for processing the recording and reproduction signal which inputs the signal to said magnetic head and reproducing the signal output from said magnetic recording medium wherein said reproduction part of the magnetic head is magnetoresistive magnetic head.
The Granular structure is that magnetic crystal grains are separated by nonmagnetic phase in a magnetic layer.
The typical crystal grain image of an embodiment of the magnetic recording medium is shown in FIG. 1 that is showing the grain boundary drawn the line along based on TEM image of the surface of magnetic layer observed by the transmission electron microscopy(TEM).
Adjoining magnetism crystal grain has been over 1 nm to each other and it is observed clearly that the nonmagnetic phase exists between crystal grain.
The shape of the magnetic crystal grain is approximately a sphere or an ellipsoid. The thickness of magnetic crystal grain (the length of the direction which is perpendicular on the surface of a film) is smaller than the thickness of the magnetic film.
However, some crystal grains with the hemisphere or the semi-ellipsoid shape in growing process near the surface of the magnetic layer may exist. Some magnetic crystal grains with the conic, hemisphere or the semi-ellipsoid shape in initial growing process may exist that grow on the crystal grain of under layer epitaxially. To get these magnetic crystal grains, hcp (hexagonal closed packed) structure which comprised of Co as a main component is used. Especially, to get higher coercive force, it is desirable that the magnetic layer includes Pt to over 20 at %. Furthermore, it is desirable that the magnetic layer are comprised of the alloy including rare earth like Nd,Sm,Pr, etc to get higher coercive force. As the alloy including rare earth, the alloy comprising of rare earth metal and transition metal which shows the high crystal magnetic anisotropy like SmCo, FeSmN, NdFeB, PrFeN is desirable and either amorphous or crystal grains can be used as the alloy.
As the nonmagnetic layer, it is possible to use oxides such as Al2O3, SiO2, Ta2O5, TiO2 and ZrO2 or non- solution elements to Co such as C and Ag, etc. The good contact start stop characteristics (the CSS characteristics) is obtained by the oxides such as Al2O3, SiO2, Ta2O5, TiO2 and ZrO2 . The corrosion resistance is more improved by the non-solution elements to Co such as C and Ag, etc.
When the ratio of coercive force which is measured in the circumferential direction to coercive force which is measured in the radial direction (orientation ratio of the coercive force) is larger than 1.0, high coercivity squareness can be obtained. When the orientation ratio of the coercive force is lager than 1.1, it is possible to suppress to reduce the reproduction output s with the progress in the time by the reduced thermomagnetism. When the orientation ratio of the coercive force is lager than 1.2, the overwrite characteristics is improved. But, it is not desirable that the orientation ratio of the coercive force is lager than 3.0 because the media noise remarkably increases.
The shape of crystal grain of magnetic layer observed by TEM observation of the surface of magnetic layer is approximate as elliptical shape. When the area ratio of the crystal grain which the extended shaft direction of this approximated elliptical shape of the crystal grain is within 30xc2x0 to the circumferential direction of the magnetic recording medium to all the crystal grain is over 45%, the high reproduction output can be obtained in the high recording density region. It is more desirable that the area ratio of the crystal grain which the extended shaft direction of this approximated elliptical shape of the crystal grain is within 30xc2x0 to the circumferential direction of the magnetic recording medium to all the crystal grain is over 60% because the DC noise can be reduced.
When the length of c axis in the radial direction is larger than the length of c axis in the circumferential direction over 1% in the case that magnetic crystal grain is the hcp structure, the effective track width extends because the turbulence of the recording magnetization is corrected.
When the average particle size is equal or more than 8nm and equal or less than 14 nm and the normalized dispersion of particle size which is normalized by the average particle size is under 0.4, the magnetic recording medium with low noise and good overwrite characteristics.
It is not desirable that the average particle size is under 8 nm because the dependency of coercive force to temperature increases very much. Also, it is not desirable that the average particle size is over 14 nm because the media noise increases.
It is desirable that the coercive force measured by applying magnetic field in recording direction (in the circumferential direction of the magnetic recording medium) is over over 2500 oersted and the product of the residual magnetic flux density Br and film thickness t (Brxc3x97t) is equal or more than 40 Gauss micron and equal or less than 120 Gauss micron (40 Gauss micron xe2x89xa6Brxc3x97txe2x89xa6120 Gauss micron) because good record and reproduction characteristic is obtained in recording density region over 1 square inch of 5 gigabits. It is not desirable that the coercive force measured by applying magnetic field in the circumferential direction of the magnetic recording medium is under 2500 oersted because record and reproduction output decreases in high recording density (over 295 kFCI) region. It is not desirable that Brxc3x97t is over 120 Gauss micron because resolution decreases and Brxc3x97t is under 40 Gauss micron because reproduction output decreases.
In this invention, Alxe2x80x94Mg alloy substrate plated the NiP( it is described as Al substrate in the following description) is used as the substrate. Also, chemically strengthened glass substrate with the strengthening layer on the surface of the substrate, crystallized glass substrate and amorphous carbon substrate, etc. can be used as the substrate.
In using Al substrate, it is desirable that the grooves like the concentric circular are not formed on the surface of the substrate by texturing because it is not good for reducing the floating height and holding the change of the floating height.
The under layer which is single layer or multilayer can be formed between substrate and magnetic layer.
The purpose of forming the under layer is to adhere the substrate to the film formed on the substrate, to control the crystal orientation of the magnetic layer and the crystal grains not too small and to prevent to come the impurity gas into the magnetic layer. The magnetic recording medium can be formed roughness on the surface and underlayer with island like roughness to improve the contact start stop characteristics ( the CSS characteristics).
Furthermore, to get the magnetic recording medium with the high reliability and high recording density, a carbon layer can be formed to 3 nmxcx9c20 nm thickness as a protective layer to the magnetism layer and a lubricant layer such as a parfluoroalkyl polyether layer etc. with the adsorption can be formed to 2 nmxcx9c20 nm thickness.
It is preferable for improving durability and corrosion resistance to use a carbon film added hydrogen or nitrogen, a film which comprises of chemical compound such as silicon carbide, tungsten carbide, (Wxe2x80x94Mo)xe2x80x94C and (Zrxe2x80x94Nb)xe2x80x94N and a mixed film including a carbon and the above mentioned chemical compound.
It is preferable that the distance between shield layers of the 2 sheets (interval of the shield layers) should be 0.30 xcexcm or less, which magnetoresistive sensor in Magnetoresistive effect type magnetic head used in magnetic storage device are located between the shield layers of the 2 sheets.
When the interval of the shield becomes over 0.30 xcexcm, the resolution reduces and the phase jitter of the signal increases. So, it is not good.
Magnetoresistive effect type magnetic head uses the magnetoresistive sensor which is comprised of plurality of electroconductive magnetic layers which magnetic directions relatively change by the external magnetic field and electroconductive nonmagnetic layer disposed between those electroconductive magnetic layers. Furthermore, by using giant magnetoresistive effect or spin valve effect, the strength of the signal can be intensified and magnetic storage device with the high reliability and the recording density over: square inch 6 gigabits can be realized.
It is variable to realize the purpose of this invention that a magnetic storage device, comprising a magnetic recording medium, a drive division that drives said magnetic recording medium in the record direction, a recording division and a regeneration division comprises magnetic head, a means that the said magnetic head is put on in the relative motion for the said magnetic recording medium, a signal processing means for carrying out signal input to the said magnetic head and output signal regeneration from the said magnetic head, the said magnetic storage device uses a medium that has a following features;
a magnetic layer in the said magnetic recording medium is formed on the substrate through monolayer or multiple underlayer, comprises said magnetic recording medium,the said magnetic layer has granular structure that the magnetic crystal grain is separated by the nonmagnetic phase, and the coercive force orientation ratio is bigger than 1.
Also, it is variable that a magnetic recording medium comprising;
a magnetic layer is formed on the substrate through monolayer or multiple underlayer, the said magnetic layer has granular structure that the magnetic crystal grain is separated by the nonmagnetic phase, in the approximation that the said magnetic crystal grain is ellipsoid, the area ratio of the crystal grain of which the extended shaft direction is within 30xc2x0 from circumferential direction is over 45%.
Also, it is variable that a magnetic recording medium comprising;
a magnetic layer is formed on the substrate through monolayer or multiple underlayer, the said magnetic layer has granular structure that the magnetic crystal grain is separated by the nonmagnetic phase and c shaft length radialy measured swells over 1% compared to a shaft length circumferentially measured.